1. Field of the invention
The present invention relates generally to headers for pressure transducers and particularly to headers for semiconductor pressure transducers suitable for high pressure applications.
2. Description of the Prior Art
Semiconductor pressure transducers are presently used in a variety of applications and are well known in the art. Such devices typically employ piezoresistive elements formed on the surface of a thin semiconductor die. The semiconductor die is mounted over an open chamber and is deflected into and out of the chamber in response to a pressure differential on its opposite planar surfaces. A change in resistance is exhibited by the piezoresistive elements in response to the deflection, whereby a signal indicative of the pressure differential is generated.
The semiconductor die is typically mounted in a header structure which serves both to isolate the semiconductor die from external stresses and to contain the pressure to be measured. Wire leads electrically connect the semiconductor die to surrounding terminal pins which extend through the header structure for connection to external electronics.
A common problem of semiconductor pressure transducers has been the sealing of the terminal pins passing through the header structure. For high pressure applications, the semiconductor die is typically mounted in a metal housing. A number of through holes are drilled in the metal housing surrounding the semiconductor die and within each hole is located an electrically conductive terminal pin. An independent glass seal is provided around each terminal pin in order to form a fluid-tight seal between the peripheral surface of the terminal pin and the interior surface of the hole. The glass seal also serves to electrically insulate the terminal pin from the metal housing.
The holes provided in the metal housing for the passage of the terminal pins are typically relatively small in diameter so that the surface area of the glass seals subjected to a pressure force is correspondingly small. The header structure is thus able to withstand high pressures without the likelihood of failure of the glass seals.
The process of drilling long, small diameter holes through the metal housing, however, adds significantly to the manufacturing cost of the header structure. In addition, the terminal pins must be located a sufficient distance apart from one another to allow for the glass seals surrounding the terminal pins. The size of the header is thereby increased, and the terminal pins are required to be located a considerable distance from the sensor die.
Thus a need exists for a header structure that does not require an independent glass seal surrounding each terminal pin and yet is suitable for high pressure applications.